Real-time motion tracking using tomosynthesis

ABSTRACT

One embodiment of the present disclosure sets forth a method for determining a movement of a target region using tomosynthesis. The method includes the steps of accessing a first set of projection radiographs of the target region over a first processing window defined by a first range of projection angles, accessing a second set of projection radiographs of the target region over a second processing window defined by a second range of projection angles, wherein the first processing window moves to the second processing window, and comparing a first positional information derived from the first set of the projection radiographs and a second positional information derived from the second set of the projection radiographs with the first positional information to determine the movement of the target region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/354,800, filed Jan. 16, 2009.

BACKGROUND

Unless otherwise indicated herein, the approaches described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Various systems and methods exist to provide radiation therapy treatmentof tumorous tissue with high-energy radiation. Many forms of radiationtreatment benefit from the ability to accurately control the amount,location, and distribution of radiation within a patient's body. Suchcontrol often includes using a multi-leaf collimator to shape aradiation beam to approximate that of the tumorous region.

Many existing radiation treatment procedures require a location of atarget region to be determined in order to accurately register thetarget region relative to a radiation source before radiation is appliedto the target region. Computed tomography (“CT”) is an imaging techniquethat has been widely used in the medical field. In a procedure for CT,an x-ray source and a detector apparatus are positioned on oppositesides of a portion of a patient under examination. The x-ray sourcegenerates and directs an x-ray beam towards the patient, while thedetector apparatus measures the x-ray absorption at a plurality oftransmission paths defined by the x-ray beam during the process. Thedetector apparatus produces a voltage proportional to the intensity ofincident x-rays, and the voltage is read and digitized for subsequentprocessing in a computer. By taking a plurality of readings frommultiple angles around the patient, relatively massive amounts of dataare thus accumulated. The accumulated data are then analyzed andprocessed for reconstruction of a matrix (visual or otherwise), whichconstitutes a depiction of a density function of a volume of the bodilyregion being examined. Cone-bream computed tomography imaging (CBCT)which uses a flat panel detector is typically used in radiation therapysystems.

CT has found its principal application in examination of bodilystructures or the like which are in a relatively stationary condition.In some cases, it may be desirable to continuously monitor a position ofa target region while a treatment procedure is being performed. However,currently available apparatus that supports CT may not be able togenerate tomographic images with sufficient quality or accuracy in partdue to intra-fraction motion caused by inadvertent patient shifts ornatural physiological processes. For example, breathing or expelling gasthrough the rectum has each been shown to cause degradation of qualityin CT images. In such cases, it would be desirable to track a movementof the target region to ensure that a treatment radiation beam isaccurately aimed towards the target region. In existing radiationtreatment systems, tracking of the target region does not use a CTimaging technique. This is because collecting a sufficient quantity ofCT image data for image reconstruction may take a long time, andtherefore may not be performed at a fast enough rate to providesufficiently current information to adjust the treatment radiation beam.

Another approach to 3D localization is “3D point tracking” which relieson taking individual projection radiographs and localizing high densityimplanted fiducial markers in each projection, for example by using thepixel coordinates of the markers' centroids. Then triangulation isperformed to find the 3D position of a marker by using differentradiographs taken at different projection angles. However, finding thepixel coordinates of a high density marker in a single X-ray projectioncan be difficult. Overlaying anatomy and external structures are animportant source of failure of these techniques. Very often, the X-rayquantum noise and scattered radiation result in the failure to detect orlocalize a marker using automatic image analysis algorithms.

Conventional portal imaging techniques use treatment “beam's-eye view”(“BEV”) imaging to track both inter- and intra-fraction motion. Onedrawback is that most BEV imaging occurs at MV energies, which is lessdose-efficient than imaging at kilo-volt (kV) energies. Another drawbackis that, if high density fiducial markers are used, the markers may notbe exposed to BEV at all times, thus causing treatment to be interruptedfor purposes of repositioning the multi-leaf collimator blades.Interruption of treatment is particularly undesirable for arc-therapies.

Some radiation therapy treatment systems are equipped with kV imagingsystems mounted to the gantry whose projection angle is orthogonal tothe treatment beam. The imaging techniques used with such an orthogonalsystem also can include CT imaging and 3D point tracking. An advantageof the kV system is its higher dose efficiency. Moreover, the imagingtarget can be exposed at all times during treatment since the kV sourceis only used for imaging. Nevertheless, the motion-related problems withfull CT acquisitions still exist as can SNR and other limitationsassociated with acquiring a single projection radiograph for 3D pointtracking.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the disclosurecan be understood in detail, a more particular description of thedisclosure may be had by reference to embodiments, some of which areillustrated in the drawings. It is to be noted, however, that thedrawings illustrate only typical embodiments and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments.

FIG. 1 is a schematic diagram illustrating a treatment radiation system,according to one embodiment of the disclosure;

FIG. 2 is a flow chart illustrating a method of performing real-timetracking using tomosynthesis, according to one embodiment of thedisclosure;

FIG. 3A is a schematic diagram illustrating a limited angle acquisitionapproach, according to one embodiment of the disclosure;

FIG. 3B is a schematic diagram illustrating another limited angleacquisition approach, according to one embodiment of the disclosure;

FIG. 3C is a side view schematic diagram illustrating yet anotherlimited angle acquisition approach, according to one embodiment of thedisclosure;

FIG. 3D is a top view schematic diagram illustrating the limited angleacquisition approach of FIG. 3C, according to one embodiment of thedisclosure;

FIG. 3E is a side view schematic diagram illustrating another limitedangle acquisition approach, according to one embodiment of thedisclosure;

FIG. 4 is a flow chart illustrating a method of acquiring projectionradiographs, according to one embodiment of the disclosure;

FIG. 5A is a flow chart illustrating a method of processing projectionradiographs using sliding arc tomosynthesis, according to one embodimentof the disclosure;

FIG. 5B is a flow chart illustrating a method of processing projectionradiographs using short arc tomosynthesis, according to one embodimentof the disclosure;

FIG. 6 is a schematic diagram illustrating an axial view of the voxelrow, according to one embodiment of the disclosure; and

FIG. 7 is a flow chart illustrating a method of adjusting treatmentreal-time, according to one embodiment of the disclosure.

DETAILED DESCRIPTION

Various embodiments are described hereinafter with reference to thefigures. It should be noted that the figures are not drawn to scale. Itshould also be noted that the figures are only intended to facilitatethe description of embodiments. They are not intended as an exhaustivedescription of the disclosure or as a limitation on the scope of thedisclosure. In addition, an aspect described in conjunction with aparticular embodiment is not necessarily limited to that embodiment andcan be practiced in any other embodiments.

FIG. 1 is a schematic diagram illustrating a treatment radiation system100, according to one embodiment of the disclosure. The treatmentradiation system 100 includes a first radiation source 102, anelectronic portal imaging device (EPID) 106, a second radiation source108 mounted on a gantry 110, a flat panel detector 114, and a controlsystem 116. The first radiation source 102 is aimed towards a patient104 and to the EPID 106. The patient 104 has markers, which may be highdensity objects that can be localized using x-ray projectionradiographs. Some examples of a marker include, without limitation, abone, a surgical clip, or other high contrast object. In one scenario,the patient 104 may have a prostate gland implanted with gold markerbeads.

In one implementation, the second radiation source 108 is situated at aright angle to the first radiation source 102. A radial direction (r)112 here is defined as the direction from the second radiation source108 through the isocenter to the flat panel detector 114. Theinformation acquired by the treatment radiation system 100 is analyzedby the control system 116, which adjusts the first radiation source 102and the rotation of the gantry 110 accordingly.

In the illustrated embodiments, the first radiation source 102 is atreatment radiation source for providing treatment energy with acollimator system for controlling a delivery of the treatment beam, andthe second radiation source 108 is an imaging radiation source. In otherembodiments, in addition to being a treatment radiation source, thefirst radiation source 102 can also provide imaging data. In otherembodiments, the first radiation source 102 can provide imaging datawithout providing treatment energy. The treatment energy generallyrefers to those energies of 160 kilo-electron-volts(keV) or greater, andmore typically 1 mega-electron-volts (MeV) or greater. The imagingenergy can include treatment energies and also energies below the highenergy range, more typically below 160 keV.

In the illustrated embodiments, the control system 116 includes aprocessor for executing instructions, a monitor for displaying data, andan input device, such as a keyboard or a mouse, for inputting data. Inthe illustrated embodiments, the gantry 110 is rotatable, and during atreatment session, the gantry 110 rotates about the patient 104, as inan arc-therapy. Here, “treatment session” generally refers to thesession in which the patient 104 is imaged and/or treated. Theoperations of the first radiation source 102, the collimator system, andthe gantry 110 are controlled by the control system 116, which providespower, timing, rotation, and position control based on received signals.Although the control system 116 is shown as a separate component fromthe gantry 110, in alternative embodiments, the control system 116 canbe a part of the gantry 110.

It should be noted that the treatment radiation system 100 should not belimited to the configuration described above, and that the system canalso have other configurations. For example, instead of the shownring-configuration, the system can include a C-arm or other types of anarm to which the first radiation source 102 or the second radiationsource 108 is secured. It should also be noted that the treatmentradiation system 100 can have one or more radiation sources. Otherconfigurations may include a single radiation source with multipledetectors, or multiple sources with a single detector.

FIG. 2 is a flow chart illustrating a method 200 of performing real-timemotion tracking using tomosynthesis, according to one embodiment of thedisclosure. In conjunction with FIG. 1, in step 202, the control system116 accesses imaging data during a treatment session. Here, “imagingdata” generally refers to projection radiographs, which as discussedabove, can come from the first radiation source 102, the secondradiation source 108, or a combination of the two sources. In step 204,the control system 116 processes the imaging data to determine 3Dinformation from the markers during the treatment session. In step 206,the control system 116 adjusts the radiation source(s) based oninformation associated with 3D positions. Here, “real-time motiontracking” broadly refers to the motion tracking that occurs while thetreatment session is ongoing. Similarly, “real-time adjustment” of thefirst radiation source 102 also broadly refers to the adjustment thatoccurs while the treatment session is ongoing. Steps 202, 204, and 206are performed concurrently with treatment and repeated until the sessionends. Each of the above steps is performed independently from the othersteps. They may also be performed simultaneously.

Before the treatment session begins in step 202, the patient 104 of FIG.1 is set-up and positioned on the treatment radiation system 100. Set-upmay involve acquiring projection radiographs to localize the markers forcomparison with digitally reconstructed radiographs from a referencescan. Alternatively, Cone Beam CT (CBCT) may be used to localize bothsoft tissue and markers. The position of the patient 104 is adjustedaccording to the localization information.

Independent from step 202, in one implementation, the gantry rotatescontinuously, and the second radiation source 108 and the flat paneldetector 114 are used to acquire projection radiographs at regularlyspaced intervals. In another implementation, the second radiation source108 and the flat panel detector 114 are used to acquire imaging datawith gaps in a certain angular range. In yet another implementation, thesecond radiation source 108 and the flat panel detector 114 are used toacquire imaging data at predetermined gantry angles. In still anotherimplementation, the control system 116 determines when the secondradiation source 108 and the flat panel detector pair 114 are used toacquire imaging data based on optimization considerations. In oneimplementation, the second radiation source 108 and the flat paneldetector 114 refer to the On-Board Imaging (OBI) system from VarianMedical Systems, Inc.

Alternatively, the first radiation source 102 and the EPID 106 cantogether also generate imaging data. For example, projectionradiographs, acquired by the EPID 106 while using the first radiationsource 102 at high energies (e.g., for treatment), may be used. Inanother example, projection radiographs, acquired by the EPID 106 whileusing the first radiation source 102 at low energies (e.g., forimaging), may be used.

In one implementation, during a treatment session, the first radiationsource 102 is configured to alternate between delivering beams fortreating a target region and delivering beams for generating imagingdata for tomosynthesis. In another implementation, a combination ofimaging data from utilizing the first radiation source 102 and thesecond radiation source 108 can be used for tomosynthesis. Inimplementations with multiple radiation sources, a combination ofimaging data from the radiation sources can be used for tomosynthesis.

The radiation source adjustment in step 206 can be done in a number ofways. For example, the collimator blades of the first radiation source102, the second radiation source 108, or the combination of the tworadiation sources of FIG. 1 can be modulated so that the markers areirradiated to minimize the extra dose delivered to the patient 104. Inaddition, the position of the collimator blades may be adjusted duringtreatment whenever the markers are determined not to be in thefield-of-view to maintain illumination of the markers. In anotherexample, the dose may vary according to the projection angle. Toillustrate, the dose for lateral views of the pelvis may be higher thanthe does for anterior-posterior views. This can be achieved either byadjusting the mAs per projection or by adjusting the projection densityor sampling rate as a function of the projection angle.

FIG. 3A is a schematic diagram 300 illustrating a limited angleacquisition approach, according to one embodiment of the disclosure. Inconjunction with FIG. 1, here, the second radiation source 108 is aimedtowards the patient 104 through to the flat panel detector 114. Thereare N projection radiographs in the sequence spanning an angular rangeΔθ 302 (also referred to as a “tomographic angle Δθ 302”.) A firstprojection angle 304 is denoted as θ_(i−N+1). A last angle 306 isdenoted as θ_(i), corresponding to current time point t_(i), which isthe most current time that imaging data is being acquired. In otherimplementations, the limited angle acquisition approach can be used bythe first radiation source 102 or other radiation sources.

As mentioned above, in one implementation, the second radiation source108 and the flat panel detector 114 pair can rotate 360° around thegantry 110 and about the patient 104 in an arcuate manner (e.g., in acounter clockwise or clockwise direction) and can generate an imageevery 1°. The second radiation source 108 and the flat panel detector114 pair may also move in tandem. In other implementations, the secondradiation source 108 and the flat panel detector 114 pair can beconfigured to rotate through a set of different rotational angles,generate a different number of images, or have gaps in the angular rangeover which the images are acquired.

FIG. 3B is a schematic diagram 320 illustrating another limited angleacquisition approach, according to one embodiment of the disclosure. Inconjunction with FIG. 1, the second radiation source 108 is aimedtowards the patient 104 through to the flat panel detector 114. Thereare N projection radiographs in the sequence spanning an angular rangeΔθ 322 (also referred to as a “tomographic angle Δθ 322”.) A firstprojection angle 324 is denoted as θ_(i−N+1). A last angle 326 isdenoted as θ_(i), corresponding to current time point t_(i), which isthe most current time that imaging data is being acquired.

In one implementation, unlike the configuration shown in FIG. 3A, thesecond radiation source 108 and the flat panel detector 114 may move indifferent directions. For example, suppose the patient 104 lays on apatient patent in an X-Y plane. The second radiation source 108 may movein a positive Y direction, while the flat panel detector 114 may move ina negative Y direction. In addition, rather than rotating 360° aroundthe gantry 110 and the patient 104, the second radiation source 108 andthe flat panel detector 108 pair may generate an image every 1° oranother rotational angle from a side of the patient 104.

FIG. 3C is a side view of a schematic diagram 340 illustrating yetanother limited angle acquisition approach, according to one embodimentof the disclosure. In conjunction with FIG. 1, the second radiationsource 108 and optionally a third radiation source 350 are aimed towardsthe patient 104 through to the flat panel detector 114.

FIG. 3D is a top view of the same limited angle acquisition approachshown in FIG. 3C, according to one embodiment of the disclosure. Thesecond radiation source 108 and the optional third radiation source 350may rotate in a circle and in a first plane above the patient 104 andthe flat panel detector 114. The flat panel detector 114 is in a secondplane, which is in parallel to the first plane. There are M projectionradiographs in the sequence spanning an angular range Δθ 342 (alsoreferred to as a “tomographic angle Δθ 342”) as the second radiationsource 108 rotates clockwise. Similarly, there are also N projectionradiographs in the sequence spanning an angular range Δθ 344 (alsoreferred to as a “tomographic angle Δθ 344”) as the third radiationsource 350 rotates clockwise. In one implementation, M may not equal toN. Also, the rotation of the one or more radiation sources may occurindependently from the rotation of a gantry, such as the gantry 110.

FIG. 3E is a side view of a schematic diagram 360 illustrating anotherlimited angle acquisition approach, according to one embodiment of thedisclosure. In conjunction with FIG. 1, the second radiation source 108and optionally a third radiation source 360 are aimed towards thepatient 104 through to the flat panel detector 114 and optionally asecond flat panel detector 362. Unlike the approach shown in FIG. 3C(i.e., the flat panel detector 114 does not rotate), the secondradiation source 108 and the third radiation source 360 may rotate in acircle and in a first plane, and the flat panel detector 114 and thesecond flat panel detector 362 may also rotate in a circle and in asecond plane. The first plane is in parallel to the second plane. As aresult, additional projection radiographs from different angular rangesmay be acquired.

FIG. 4 is a flow chart illustrating a method 400 of acquiring projectionradiographs, according to one embodiment of the disclosure. Using theapproach shown in FIG. 3A as an example, in step 402, a processingwindow is defined by the tomographic angle Δθ 302. In oneimplementation, the processing window can range from 3° to 40°. Themethod 400 can be carried out by the first radiation source 102, thesecond radiation source 108, or other radiation sources in otherimplementations.

In conjunction with FIG. 1, in step 404, the control system 116 accessesthe imaging data within the processing window taken from time t_(i−N+1)to t_(i), corresponding to the N projection radiographs taken betweenprojection angles θ_(i−N+1) 304 to θ_(i) 306 in FIG. 3A. As an example,for a sliding arc window, the control system 116 accesses 21 projectionradiographs taken between projection angles 20° and 40° (1 projectionradiograph taken at each degree interval). In step 406, at time t_(i), awindow of N projection radiographs starting at time t_(i−N+1), isprocessed. Two methods of processing the windows of projectionradiographs, sliding arc tomosynthesis and short arc tomosynthesis, arefurther described in conjunction with FIGS. 5A and 5B below.

Continuing with FIG. 4, in step 408, the control system 116 moves on tothe next processing window (i=i+1). The moving of the processing window302 may occur while treatment is still ongoing so that at the next timeincrement t_(i+1) the projection radiograph at time t_(i−N+1) may bedropped. If the coordinates of the backprojection matrix do not rotatein place with the acquisition, then processing may continue bysubtracting the projection radiograph at t_(i−N+1) and adding theprojection radiograph at time t_(i+1). In the above sliding arc example,at the next time increment, the projection radiograph at the projectionangle 20° is dropped, and the new projection radiograph taken at thistime increment, corresponding to projection angle 41°, is added. Inother words, the processing window 302 slides to encompass projectionangles 21° through 41°. Steps 404, 406, and 408 are repeated throughoutthe treatment period. In the example above, 21 projection radiographsfrom 21° to 41° are first processed. Then 21 projection radiographs from22° to 42° are subsequently processed, and so on, with the 20°processing window sliding over 1° at each time increment. In an optionalstep 410, the movement of the processing windows ends when treatmentends.

FIG. 5A is a flow chart illustrating a method 500 of processingprojection radiographs using sliding arc tomosynthesis, according to oneembodiment of the disclosure. The method 500 can be carried out by thefirst radiation source 102, the second radiation source 108, or otherradiation sources in other implementations. Step 502 corresponds to step202 of FIG. 2 and step 404 of FIG. 4. In conjunction with FIG. 1 and theexample above for sliding arc tomosynthesis, the control system 116accesses 21 projection radiographs for each 20° processing window. Steps504, 506, and 508 further illustrate steps 204 and 406. At time t_(i), awindow of N projection radiographs starting at time t_(i−N+1), isprocessed. In step 504, reconstruction using techniques such as, withoutlimitation, backprojection or filtering. Step 504 can also includepreprocessing techniques, such as, without limitation, performinglogarithmic transforms. When more than one radiation source and/or morethan one flat panel detector are utilized to acquire the radiographprojections (e.g., the approaches illustrated in FIGS. 3C, 3D, and 3Eand discussed above), in one implementation, the different radiographprojections generated from distinct radiation source and flat paneldetector pairs are processed using, for example, filtering andbackprojection operations, to reconstruct an image. Other reconstructionmethods may involve iterative techniques.

Backprojection is a common algorithm used in the tomographicreconstruction of clinical data. When an n-dimensional object isprojected, each projection radiograph is an n−1 dimensional sum of itsdensity along the projection axis. The reverse function is called backprojection and regenerates the original object. In some implementations,the orientation of the backprojection matrix may rotate with the imageacquisition system, which is a more “natural” coordinate system fortomosynthesis reconstruction. Here, the radial direction is defined asbeing parallel to the central projection angle θ_(p)=(θ_(i−N+1)+θ_(i))/2of the imaging system and a lateral direction as being orthogonal to theradial direction. For tomosynthesis reconstruction, two axes of thebackprojection (or reconstruction) matrix are in lateral directionswhile the third axis is directed in the radial direction which ingeneral, has lower spatial resolution than the lateral axes. Inalternative implementations, the backprojection matrix can be fixed inthe normal Cartesian coordinate system (e.g., left-right,anterior-posterior, superior-inferior) used for imaging andradiotherapy. One common method of backprojection is known and “shiftand add tomosynthesis.” In particular, the projection radiographsacquired using the approach described in conjunction with FIG. 4 aboveare shifted and added in the plane of interest to bring the markers infocus, while structures in other planes are distributed and thus appearblurred.

Before backprojection is performed, the data may be processed to enhancecertain spatial frequencies and depress others. An example is thefrequency-domain ramp filter that is used for the Feldkamp, Davis, andKress (FDK) reconstruction algorithm. Compensation may be made for 1/r²effects as prescribed by the FDK algorithm. After backprojection, thedata may be filtered to deblur the image. Deblurring techniques caninclude spatial frequency filtering selective plan removal, iterativerestoration, matrix inversion, or other techniques known in the art.

In some implementations, fully iterative reconstruction methods are usedwhere the data are first backprojected and then forward projected forcomparison with the original projection radiographs. Examples ofiterative techniques include, but are not limited to, ART, EM MLEM, andOSEM.

In step 506, the positions of the markers are determined. In oneimplementation, a different method is employed to identify the axisalong the radial direction for the markers than the axes along thelateral directions. Some techniques for detecting the markers include,without limitation, calculating the 3D center-of-mass of each marker,curve fitting, or peak finding. In step 508, an average shift isdetermined based on how the markers have moved relative to theirposition just before treatment starts. This original or startingposition may be determined using multiple techniques including but notlimited to CBCT or tomosynthesis involving the first and/or secondsource-detector pair.

FIG. 5B is a flow chart illustrating a method 550 processing projectionradiographs using short arc tomosynthesis, according to one embodimentof the disclosure. The method 550 can be carried out by the firstradiation source 102, the second radiation source 108, or otherradiation sources in other implementations. Like FIG. 5A, Step 552 alsocorresponds to step 202 of FIG. 2 and step 404 of FIG. 4. However, as avariant of the sliding arc tomosynthesis approach described above, thearc length can be smaller for marker tracking using short arctomosynthesis. As an example, the control system 116 of FIG. 1 heregenerally accesses 6 projection radiographs for each 3° processingwindow. The angular range of a processing window for short arctomosynthesis can be approximately 3 degrees or may correspond to acompromised larger arc length to include approximately minimum 6projection radiographs. Steps 554, 556, 558, 560 and 562 furtherillustrate step 204 of FIG. 2 and step 406 of FIG. 4. Similar to FIG.5A, the reconstruction performed in step 554 also may include techniquessuch as, without limitation, backprojection or filtering, and thepreprocessing techniques possibly utilized in step 554 includetechniques such as, without limitation, performing logarithmictransforms.

In step 554, in one implementation, when short arc tomosynthesisreconstructs small volumes, a number of slices are generated by backprojecting the input projection radiographs without putting them through2D spatial filtering. The depth covered by these slices cover severaltimes the depth of the volume of interest. In such an implementation, a3D filter can be applied to the generated slices to remove the blurredout-of-slice structures for the slices of interest. This method isdescribed in the United States Patent Application No. US 2007/0237290 A1of Varian Medical Systems, Inc.

In step 556, the control system 116 creates an enhanced 2D image. Unlikethe sliding arc tomosynthesis approach of FIG. 5A, which generates 3Dinformation, this short arc tomosynthesis approach combines projectionradiographs acquired over a small arc of gantry rotation to generate a2D image with significant enhancement of the target region. This 2Dimage is used instead of the original projection radiographs for markertracking. Steps 552, 554, and 556 are repeated at least once, using adifferent short arc window, in order to generate multiple 2D images. Inone implementation, this short arc can “slide” as in sliding arctomosynthesis, and the imaging data corresponding to the short arc maybe acquired continuously. In another implementation, the imaging datacorresponding to the short arc may be acquired with gaps in a certainangular range. In yet another implementation, the imaging datacorresponding to the short arc may be acquired at predetermined gantryangles. In still another implementation, the control system 116 of FIG.1 may determine when to access the imaging data corresponding to theshort arc based on optimization considerations.

Before describing step 558 of FIG. 5, FIG. 6 is a schematic diagram 600illustrating an axial view of a voxel row, according to one embodimentof the disclosure. For the purpose of 3D tracking, short arc DTS voxels602 can be visualized in the planes that are parallel to the imagerrotation axis (also referred to as “slice planes” or “lateral planes”)and normal to the imaging axis at a center projection 604 of anacquisition arc 606. The voxel dimensions are small in the slice planeand long in the direction parallel to the imaging axis at the arc center(i.e. the radial direction). The long voxel dimension, or large “voxeldepth,” corresponds to low depth resolution, and is due to the short arcused for tomosynthesis. Depth resolution is determined by triangulation,and is not an objective of individual images. Short arc tomosynthesisenhances the image of markers in the presence of noise and reduces theeffect of overlaying objects outside the volume occupied by the markers.For example, in the case of multiple markers in prostate, the voxeldepth can be about 2 to 3 cm, thus minimizing the effect of anyoverlaying bony structures or external objects. This voxel depth isachievable with short arcs of 2 to 3 degrees.

Referring back to FIG. 5, in step 558, the control system 116 performstriangulation using multiple 2D images generated from step 556. Threedimensional tracking by triangulation uses two or more images that arereconstructed from short arcs centered at different gantry angles.Geometrically, the 2D images of the markers can be viewed as projectionradiographs of the markers onto a new image plane that is defined by theslice plane 602. In one implementation, triangulation using two of theseimages can be achieved by intersecting the two lines that go through the2D position of the target, found in each image, and where each line alsoconnects to the radiation source position for the corresponding arccenter. This intersection of the two lines is also referred to as atriangulated position. In such an implementation, the geometriccalibration parameters of each 2D image can vary with the gantry anglecorresponding to the short arc center; the source-to-image planedistance is the normal distance of the radiation source positioncorresponding to arc center, to the slice plane; this is different fromsource-to-flat panel (physical image sensor) distance and can vary withthe gantry angle corresponding to short arc center. Similar to FIG. 5A,3D information is determined in step 560, and the average shift iscalculated in step 562.

FIG. 7 is a flow chart illustrating a method 700 of performing real-timetreatment adjustment, according to one embodiment of the disclosure. Inone implementation, after the control system 116 of FIG. 1 calculates anaverage shift as shown in FIG. 5A and FIG. 5B and discussed above, driftdata for tracking or repositioning based on the average shifts from twoprocessing windows are also calculated. Specifically, in oneimplementation, the control system 116 determines whether low frequencymotion has occurred in step 702. If low frequency motion is indeeddetected, the control system 116 is configured to use linear predictionmethods to compensate for the temporal delay in step 704. The averagetemporal delay in seconds (T_(r)) in the radial direction is given bythe equation T_(r)=NΔt/2, where N is the number of projectionradiographs processed, and Δt is the sampling period of the projectionradiographs. In step 706, the drift data is fed back to the treatmentsystem. In step 708, the multi-leaf collimator will be adjusted so thatthe first radiation source 102 is directed to compensate for the drift.

If in step 702 the control system 116 instead determines that atransient motion has occurred, then in step 710 treatment is stoppeduntil the transient motion dissipates. In step 712, the control system116 determines whether the transient motion has returned to the initialposition. If so, the drift data is fed back to the treatment system andthe multi-leaf collimator will be adjusted, in steps 706 and 708,respectively. If not, in step 714, the control system 116 can acquire abeam's eye projection from the first radiation source 102 to resetmarker positions in the radial direction. After the marker positions arereset, the drift data is again fed back to the treatment system in step706 and the multi-leaf collimator is adjusted to compensate the driftdata in step 708.

In other embodiments, in conjunction with FIG. 1, the control system 116is configured to not only adjust treatment beams from the firstradiation source 102, but also interleave imaging beams from the secondradiation source 108, imaging beams from the first radiation source 102,treatment beams from the first radiation source 102, and other datasignals.

In the illustrated embodiment, the methods 400, 500, and 550 can beperformed while treatment occurs. In an alternative implementation, themethods 400, 500, and 550 can be performed using the projectionradiographs acquired prior to a current treatment session. In someimplementations, in conjunction with FIG. 1, the 3D information of themarkers determined using the methods 500 and 550 can also be used toverify a location of a target region, to track a movement of the targetregion, and/or to control an operation of the first radiation source102, and/or the collimator. In the illustrated embodiment, the method700 adjusts the multi-leaf collimator in real-time during treatment. Inother implementations, the method 700 can adjust gantry speed, deliverydose, or other treatment parameters.

One embodiment of the disclosure may be implemented as a program productfor use with a computing device. The programming instructions of theprogram product define functions of the embodiments (including themethods described herein) and can be contained on a variety ofcomputer-readable storage media. Illustrative computer-readable storagemedia include, but are not limited to: (i) non-writable storage media(e.g., read-only memory devices within a computer such as CD-ROM disksreadable by a CD-ROM drive, DVD disks readable by a DVD driver, ROMchips or any type of solid-state non-volatile semiconductor memory) onwhich information is permanently stored; and (ii) writable storage media(e.g., floppy disks within a diskette drive, hard-disk drive, CD-RW,DVD-RW, solid-state drive, flash memory, or any type of random-accessmemory) on which alterable information is stored. Such computer-readablestorage media, when carrying computer-readable instructions that directthe functions of the present disclosure, are embodiments of the presentdisclosure.

While the foregoing is directed to embodiments of the disclosure, otherand further embodiments of the disclosure may be devised withoutdeparting from the basic scope thereof. Therefore, the above examples,embodiments, and drawings should not be deemed to be the onlyembodiments, and are presented to illustrate the flexibility andadvantages of the disclosure as defined by the following claims.

We claim:
 1. A method of determining a movement of a target region usingtomosynthesis, comprising: accessing a first set of projectionradiographs of the target region over a first processing window definedby a first range of projection angles; accessing a second set ofprojection radiographs of the target region over a second processingwindow defined by a second range of projection angles, wherein some ofthe first range of projection angles in the first processing windowoverlap with the second range of projection angles in the secondprocessing window; and comparing a first positional information derivedfrom the first set of the projection radiographs and a second positionalinformation derived from the second set of the projection radiographs todetermine the movement of the target region.
 2. The method of claim 1,wherein the first set of projection radiographs and the second set ofprojection radiographs are acquired by rotating a first radiation sourceand a first flat panel detector about the target region in an arcuatemanner.
 3. The method of claim 1, wherein the first set of projectionradiographs and the second set of projection radiographs are acquired bymoving a first radiation source that aims at the target region in afirst direction and moving a first flat panel detector in a seconddirection.
 4. The method of claim 3, further comprising moving the firstradiation source and the first flat panel detector along sides of thetarget region.
 5. The method of claim 1, wherein the first set ofprojection radiographs and the second set of projection radiographs areacquired by rotating a first radiation source that aims at the targetregion in a first plane, wherein the first plane is in parallel to asecond plane that a first flat panel detector is in.
 6. The method ofclaim 1, wherein the first set of projection radiographs and the secondset of projection radiographs are acquired by rotating a first radiationsource that aims at the target region in a first plane and rotating afirst flat panel detector in a second plane.
 7. A treatment systemconfigured to determine a movement of a target region usingtomosynthesis, comprising: a rotatable gantry; a first radiation source;a first flat panel detector; and a control system, wherein the controlsystem is configured to access a first set of projection radiographs ofthe target region over a first processing window defined by a firstrange of projection angles; access a second set of projectionradiographs of the target region over a second processing window definedby a second range of projection angles, wherein some of the first rangeof projection angles in the first processing window overlap with thesecond range of projection angles in the second processing window; andcompare a first positional information derived from the first set of theprojection radiographs and a second positional information derived fromthe second set of the projection radiographs with the first positionalinformation to determine the movement of the target region.
 8. Thetreatment system of claim 7, wherein the control system is furtherconfigured to rotate the first radiation source and also the first flatpanel detector about the target region in an arcuate manner to acquirethe first set of projection radiographs and the second set of theprojection radiographs.
 9. The treatment system of claim 7, wherein thecontrol system is further configured to move the first radiation sourcethat aims at the target region in a first direction and move the firstflat panel detector in a second direction to acquire the first set ofprojection radiographs and the second set of the projection radiographs.10. The treatment system of claim 9, wherein the control system isfurther configured to move the first radiation source and the first flatpanel detector along sides of the target region.
 11. The treatmentsystem of claim 7, wherein the control system is further configured tomove the first radiation source independently from rotation of therotatable gantry to acquire the first set of projection radiographs andthe second set of the projection radiographs.
 12. The treatment systemof claim 7, wherein the control system is further configured to rotatethe first radiation source that aims at the target region in a firstplane, which is in parallel to a second plane that the first flat paneldetector is in, to acquire the first set of projection radiographs andthe second set of the projection radiographs.
 13. The treatment systemof claim 7, wherein the control system is further configured to rotatethe first radiation source that aims at the target region in a firstplane and rotate the first flat panel detector in a second plane toacquire the first set of projection radiographs and the second set ofthe projection radiographs.
 14. A computer readable medium containing asequence of programming instructions for determining a movement of atarget region using tomosynthesis, which when executed by a processor ina treatment system, causes the treatment system to: access a first setof projection radiographs of the target region over a first processingwindow defined by a first range of projection angles; access a secondset of projection radiographs of the target region over a secondprocessing window defined by a second range of projection angles,wherein some of the first range of projection angles in the firstprocessing window overlap with the second range of projection angles inthe second processing window; and compare a first positional informationderived from the first set of the projection radiographs and a secondpositional information derived from the second set of the projectionradiographs with the first positional information to determine themovement of the target region.
 15. The computer readable medium of claim14, further comprising a sequence of programming instructions, whichwhen executed by the processor, causes the treatment system to rotate afirst radiation source and a first flat panel detector about the targetregion in an arcuate manner to acquire the first set of projectionradiographs and the second set of the projection radiographs.
 16. Thecomputer readable medium of claim 14, further comprising a sequence ofprogramming instructions, which when executed by the processor, causesthe treatment system to to move the first radiation source that aims atthe target region in a first direction and move the first flat paneldetector in a second direction to acquire the first set of projectionradiographs and the second set of the projection radiographs.
 17. Thecomputer readable medium of claim 16, further comprising a sequence ofprogramming instructions, which when executed by the processor, causesthe treatment system to move the first radiation source and the firstflat panel detector along sides of the target region.
 18. The computerreadable medium of claim 14, further comprising a sequence ofprogramming instructions, which when executed by the processor, causesthe treatment system to rotate the first radiation source that aims atthe target region in a first plane, which is in parallel to a secondplane that the first flat panel detector is in, to acquire the first setof projection radiographs and the second set of the projectionradiographs.
 19. The computer readable medium of claim 14, furthercomprising a sequence of programming instructions, which when executedby the processor, causes the treatment system to rotate the firstradiation source that aims at the target region in a first plane androtate the first flat panel detector in a second plane to acquire thefirst set of projection radiographs and the second set of the projectionradiographs.